In a case where an airbag is mounted at a vehicle so as to protect an occupant of a seat for the vehicle (i.e., the vehicle seat), for example, an occupant detection system is provided at the vehicle seat to thereby detect the occupant of the vehicle seat. Such occupant detection system is disclosed in JPH09-207638A. The occupant detection system disclosed in JPH09-207638A detects the occupant of the vehicle seat based on a magnitude correlation between a detection load value obtained by a load sensor provided at the vehicle seat and a predetermined threshold value stored beforehand at a read-only storage unit of a microcontroller unit (MCU) such as a UV-EPROM.
According to the occupant detection system, a threshold value serving as a constant may change in association with an implementation of a vehicle evaluation. In a case of the change of the threshold value, software is modified so as to change the constant of program stored in the read-only storage unit of the microcontroller unit. Such program change involves a drawing change of the microcontroller unit. That is, various types of programs, each of which is stored in the read-only storage unit of the microcontroller unit, are present while having different constants from one another. Accordingly, the number of types of the controller units for the occupant detection system increases in association with the number of different threshold values (i.e., the number of constants of the respective programs) stored in the read-only storage unit, which may lead to an increase of a management cost.
A need thus exists for a storage unit for an occupant detection system which is not susceptible to the drawback mentioned above.